The NetGetDCName function returns the name of the primary domain controller (PDC). It does not return the name of the backup domain controller (BDC) for the specified domain. Also, you cannot remote this function to a non-PDC server.

static extern NetApiStatus NetGetDCName(string serverName, string domainName, out IntPtr buffer);

Private Shared Function NetGetDCName(ByVal serverName As String, ByVal domainName As String, ByRef buffer As IntPtr) As NetApiStatus

NetApiStatus result = NetGetDCName(null, null, out domainInfo);

Dim result As NetApiStatus = NetGetDCName(Nothing, Nothing, domainInfo)

Documentation

[NetGetDCName] on MSDN

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